Photographic objective



on 2.927.so

1" WO F March 8, 1960 DETERMANN 2,927,506 PHOTOGRAPHIC OBJECTIVE FiledSe t... 9, 1957 v s Shoots-Sheet 1 T Z r. 3/ 2 A 3/ INVENTOP FRHZDETERMANN ATV RN ETS "March 8, 1960 F. DETERMANN PHOTOGRAPHIC omc'nvs 3Shasta-Shut 2 Filed Sept. 9, 1957 FIG 2 uwswrae FR T DETERMAN March 8,1960 F. DETER'MANN PHOTOGRAPHIC OBJECTIVE 3 Sheets-Sheet 3 Filed Sept.9. 1957 INVENI'OR FRITZ DETERNAN ATYORNEYS United States PatentPHOTOGRAPHIC OBJECTIVE Fritz Determann, Braunschweig, Germany, assignorto Voigtliinder A.G., Braunschweig, Germany, a corporation of GermanyApplication September 9, 1957, Serial No. 682,808

Claims priority, application Germany September 12, 1956 6 Claims. (Cl.88-57) This invention relates to photographic objectives having a largeimage angle and has particular relation to such photographic objectivesof the enlarged triplet-type having high light-transmitting power and along back focal length which is in the range of 85% and 125% of theequivalent focal length.

This invention represents a further development of objectives accordingto the US. Patent No. 2,746,351. On the side of the longer conjugate, adiverging meniscusshaped front member is arranged, the surfaces of whichare concave toward the diaphragm and which is separated from thesubsequent converging system by a distance which is smaller than of theequivalent focal length of the pivotal objective, whereby the convergingsystem is a triplet variation provided with a preceding additionallyinserted converging lens.

Photographic objectives of the above outlined general structure have, ingeneral, at a useful correction of the spherical zonal aberrations andof the central curving of the image, still noticeable astigmaticadjustment differences between the sagittal and meridional image shellsand, at the same time, higher comatic residual aberrations in thelateral portions of the image field. Thereby, in general, the astigmaticadjustment difference, which affects the image structure, is the higher,the larger the back focal length of the objective is selected relativeto the equivalent focal length and the more the optical designerendeavors corrections with small zonal aberrations. The above mentionedadditional converging lens L which is inserted in front of the triplet,contributes to the reduction of zonal aberrations of the aperturaldefects. However, with increasing improvement of the image performanceof widely open pencils of rays, the presence of residual astigmaticadjustment differences has particularly undesired effects in the lateralimage portions. The elimination of these defects, without the use ofextremely strong surface curvatures (e.g. surfaces having a, nearlyhemispherical shape) could not be attained in the structures hithertosuggested.

It has now been found that by proceeding according to the presentinvention the image performance can be considerably improved, and theimage extensively freed from the beforementioned astigmatic defects.According to the present invention, the distribution of refractive powerwithin the total objective in the adjacent pair of surfaces (R R betweenthe diverging lens (L which is enclosed in the converging main system IIand is of unequal curvature of the surfacesand the strongly refractiveconverging lens (L which precedes it on the side of the longerconjugate, is selected in the following manner: The absolute value ofthe sum of the two surface refractive powers (t +p of these two adjacentsurfaces is greater than A of the equivalent refractive power t) of thetotal system, without, however, exceeding the value of A of this totalrefractive power. If this upper limit is exceeded, then again saidundesired progressive increase of the astigmatic adjusting diflerenceoccurs in the zonal ranges of the out-of-axis image field.

This increase adversely affected production of the image in olderconstructions, while at values below said lower limit the aperturalaberrations are so strongly increased that only small relative aperturescan be successfully utilized, i.e. the useful light-transmittingcapacity of such systems will be noticeably reduced.

This first condition of the present invention is expressed by thefollowing formula:

Due to the connection between refractive power and surface curvature inthe range of the refractive indices of conventional glasses, the aboveFormula 1 represents a guide also with regard to the selection of thecurvature of this pair of adjacent surfaces, because this selection ofcurvature yields also the possibility of favorably affecting the zonalaberrations of widely open extra-axial pencils. The curvature of a glassor air lens--i.e. of a vicinal pair of surfaces-4s defined, in a mannerknown by itself, by the sum of radii on the one hand and the differenceof radii on the other hand, or by the sum of refractive powers on theone hand and the difference of refractive powers on the other hand.Accordingly, the second condition of the present invention consists inthat the absolute value of the difference of this vicinal pair ofsurfaces (ga -(p is larger than A: of the equivalent refractive power Iof the total system, but does not exceed 3/2 of this total refractivepower. This second condition according to the invention is expressed bythe following formula:

By observing this second condition, it is additionally possible toobtain a particularly good extra-axial zonal correction of aperturaldefects, whereby practical utilization of high, relative beam openingsis secured also for the lateral image.

In this manner according to the invention, an increased power of theobjective and at the same time an improved quality of the image byreduction of astigmatic and comatic aberrations is obtained.

An increase of the relative-aperture of optical systems at predetermineddimensions, and thus for predetermined diameters of the lenses, alwaysmeans an increase of the refractive powers of the converging elementsand in this connection a further condition of the present invention,which relates to the additional converging lens L,, is used. The sum ofrefractive powers of the surfaces of this lens, should be linked withthe absolute value of the sum of surface refractive powers of thebeforementioned characteristic pair of vicinal surfaces in such a mannerthat the quotient of the absolute value of the sum of refractive powers(t of the pair of vicinal surfaces (R R divided by the sum of surfacerefractive powers (g0 +zp of this converging lens L is in the rangebetween 0.25 and 1.25.

This condition-expressed by the corresponding reciprocal value-meansthat the sum of surface refractive powers of lens L (i.e. its elementarylens refractive power) constitutes a positive refractive power portionof the total refractive power of the objective, which is more than ofthe absolute value of the sum of surface refractive powers of saidcharacter- 'istic pair of vicinal surfaces (R 7), whereby, however, thelens refractive power of lens L is smaller than the fourfold of saidabsolute value. A too strong com verging effect of lens L would toostrongly reduce the influence of the pair of vicinal surfaces and this,in turn, would result in an increase of the astigmatic adjustmentdifference. This condition of the present ink rtml (3) V 0.25 WM 1.25

In order to correct-in an objective designed in conformity with theabove conditions-the distortion to particularly small residual amounts,it has been found advisable to tune the curvature of the four lenseslocated in front of the diaphragm, in a specific relation. According tothe latter, the absolute value of curvature of the negativemeniscus-shaped front lens (L represented by the quotient of therefractive power difference (r divided by the refractive power sum t-(in relation to the distance (a between this negative lens (L and thesubsequent converging lens (L should have a value which is in the rangebetween the fourfold and the ninefold of the value of the equivalentrefractive power (d of the total objective. This condition is expressedby the following formula:

In addition, simultaneously, the relation between (a) the absolute ratioof the curvature of the second lens (L =L of the system, to thecurvature of the third lens (L )and (b) the absolute ratio of thecurvature of this third lens, to the curvature of the fourth lens (L)-should correspond to at least 1:1, but should not exceed 3:1. If thecurvature of a lens having surfaces i and k is denoted the aboveoutlined condition can be expressed by the following formula:

It is within the scope of the present invention to design the negativemeniscus-shaped front member (I) as a single lens, without adverselyaffecting the image performance. The expenses of manufacture are therebyconsiderably reduced, particularly in view of the fact that this lensshould have a particualrly large diameter.

Without adversely affecting the image performance, the three lenses ofthe converging triplet, preceding the diaphragm, can likewise consist ofuncemented single lenses (L L L In connection with the correction ofextra-axial aberrations, it has been found advisable to design theconverging lens (L3), which precedes the diverging lens (L4), with arelatively large central thickness. The range of 10%-25% of theequivalent focal length of the total objective has been found to beparticularly advantageous in this connection.

It has been further found that a favorable influence on the aperturaldefects of the total system can be obtained by having in the rear memberwhich follows the diaphragm, a cemented surface (of the type known byitself in triplet variations) which is convex toward the diaphragm.

The particular advantage of wide angle objectives of the presentinvention, which have a long back focal length, consists in the increaseof the relative aperture to values above 1:4, with a simultaneousimprovement of the correction of extra-axial image defects.

The following examples describe some specific embodiments and best modesof carrying out the invention, to which the invention is not limited.

In the first of these examples, the above mentioned convergingadditional lens L, consists of a very strongly curved meniscus, bothradii of which are considerably smaller than the equivalent focal lengthof the total objective. In the second example, the radii of this lens L,are considerably flatter, i.e. this lens is designed as a relativelyweakly curved meniscus. Finally, in the third example the lens L isdesigned as a biconvex lens of unequal curvature. In Example 2, theconverging component of the characteristic pair of vicinal surfaces (R Ris the rear surface of a converging lens on the side of the longerconjugate, the refractive index of said lens being larger than that ofthe subsequent diverging lens L In Example 3, which illustrates a higherlight intensity, the refractive index of the individually arrangeddiverging lens L is larger than that of the preceding converging lens,so that thereby the diverging partial component of the refractive powerof the diverging pair of vicinal surfaces has a higher refractive indexthan the converging component. Furthermore, in Examples 1 and 2, themeniscus-shaped diverging front lenses (I) of the total system are madeof very low-refractive glasses (refractive index of about 1.5), while inExample 3 this negative front meniscus I is made of highly refractiveglass (n 1.6). Furthermore, in Example 1 the radius of curvature of thesurface, which follows the diaphragm in the direction of light, has apositive sign, while this sign is negative in Examples 2 and 3. InExample 3, this surface is particularly strongly curved.

These examples demonstrate that within the scope of the presentinvention considerable variations are available to the designer withregard to the selection of the additional correction elements. Thus, forexample, the selection of the glass in the rear member (which limits thetotal objective on the side of the shorter conjugate) on the image side,was done in such a manner that in this rear member there is a differenceof the refractive indices between its two individual components, whichamounts to about 0.08 in Examples 1 and 2 and in the objective ofhighest power according to Example 3, to about 0.04, i.e. is reduced toabout the half. If the optical designer continues to proceed in thisdirection, he will arrive at a difference of refractive indices of 0 andthis would result in an individual (i.e. not composite) positive memberwhich concludes the total objective on the side of the shorterconjugate.

In the appended drawings-which are illustrated for a focal length of ;f=mm.the meaning of the reference symbols is as follows:

R=the radii of curvature of the individual lens surfaces, =the distancebetween the vertexes of the lens surfaces, a=the distances between theaxes of the individual lenses,

said symbols being numbered-in conformity with the symbols used in thetablesin the same manner as the lenses L, from the side of the longerconjugate toward the side of the shorter conjugate. The glasses used arecharacterized by the refractive indices n for the yellow light of thed-line of the helium spectrum having a wave length of A=5876 angstromunits and by the Abbe number y for the color dispersion. The diaphragmis denoted by reference symbol B in the drawings.

In the appended drawings Figure 1 illustrates the scheme of referencesymbols;

Figure 2 corresponds to the embodiment according to the data of Example1;

Figure 3 corresponds to the embodiment according to the data of Example2;

Figure 4 corresponds to the embodiment according to the data of Example3.

, In the following examples, in connection with each surface, thesurface refractive power is additionally stated for the surface numberi. In these tables (which refer to the focal length i=1) the back focallength is denoted by reference symbol s',,. As the (4) 4I 6.70051 9 Iequivalent refractive power of the total system is equal to thereciprocal value of the focal length, the former is (V) D,=- =4.125055also equal 1-. in the examples.

' Example I [f-LOOOO 1:3,4 xii-1.0403.)

Ri =+0.90sa02 m -+0.66ma6 6, =0. 06217 i=1. 50137; 71-56. 5 R,=-+0.470316 w =-l.066028 a; =0. 46976 air Ra =+0. 535531 s ='+1- 2407 061-0. 04698 m=1. 664466; 35.9 R4 ==+0.878265 104 =-0.756660 aa=0.00497air R6 -+0.446276 w =I+1. 397665 d,=0. 10639 m=1. 62374; 16=41. 0 R6=-5.860994 :pa =+0.106422 at=0.033l6 air R1 ==0. 967161 p7 ==0. 627786d4=0. 01603 m=1. 60717; v4=40. 2 R, =+o.a41792 m =1.7764a1 (xi-0.06356air, diaphragm space R9 =+s4. 585115 4 =-+0.007290 (iv-0. 01382 m-i.61659; I=36. 6 Rm==+0. 332924 1u=-1- B52044 a6=0. 00000 Cemented surfaceRn=-|-0.332924 11=+2.075549 116 0. 15476 m=1. 69100; Vfl=54. s R z= 0.570625 1l=+ 210953 The above data show: D3: 6;e: (I) 1 ,[=0.s21364 andthus at 1 =1 P7-t s (II) Furthermore, =4 805018 ]=0.734208 and thus D30- 48 0.5 0.734208 1.5 (2) 66 i: g- ?;2=1.796693 (111) Moreover, l .4

2 l|pfl+1l=0-521364 and 4 805018 so that 40 D and thus I D4 a+t m and(5) 1 2.674070 3 3 025 1076776 125 In the objective characterized by theabove numerical data of Example I the following tolerances can be used(IV) Furthermore, with practically equal correction effects:

D1=:::%:':': i f; d= :l: 0.05,; a iuos Example 2 R1 =+0. 898582 n =+0.551957 R =+0 460m di=0.06208 m=1.50137; v1=56.5 l 088801 R2 -+1 08214549624 air so: -+0045956 :+3'662309 d:-=0.04690 m=1. 66072; 16:16.4O'182049 R +0 491656 Mr W +1 261960 2'763148 61-0. 179341L3=1.62045;v3=38.0 :+0'224545 393F885 a;==0.02 759 air 0'644759d|=0.01600 m=1.60342;m=38.0 1'753883 RE 4 0 4708 a4=0.06346 air,diaphragm space w 0 15139 ()282 3 d,=0.013s0 n;,=1.61293; 115=37.0 2'166il) 82:3 as=0. 00000 cemented surface il 2 4512::

0=0-15313 m=1.60350; v6=53.4 011* R1z=-0.527964 n=+1.313537 at |1'-t2l=and v 1+g=0514042 The above data show:

. v thus at 0 6976 so that (1) 0.25 0.420Z14 0.75 D1 3 147630 u[=0.869304 and thus H 0.46' 976 :670051 and thus 0.5 0.869304 l.5

In the objective characterized by the above numerical data of Example 2,the following tolerances can be used with practically equal correctionelfects:

8 a =O.65606 so that L =4.23ss2 and thus & 1.594995 "1.241666 In theobjective characterized by the above numerical data of Example 3, thefollowing tolerances can be used =1.28456, so that with practicallyequal correction effects:

A,. 0.2 1. A photographic objective of the extended triplet type, R f da 5:0 05f having a long back focal length m the range of 85% and Example3 [f=1.0000 1:2,8 flu-1.05%.]

R =+1. 260617 (pr ==+0.494789 d1 =0. 06213 m =1. 02374; n =47. 0 Rs==+0. 593764 40: =-1.050485 a =0.65606 air Rs +1. 152130 m =+0. 578685 d=0. 06903 'II-Fl- 66672; "'84. 4 R4 =11. 275279 w =+0.059131 aa=0. 02209air Rs ==+0. 522802 9 5 =+1. 186778 da=0. 19880 m=1. 62045; vz=38. 0 Rs==1.614186 m =+0-384373 aa=0. 02209 air R7 =-0. 879878 p7 =0. 710735d4=0. 03424 n4==1. 62536; =35. 6 Rs =+0. 367016 1 pg =1.703904 a4=0.08560 air; diaphragm space R9 =-1.924128 10a =-0. 338481 115 =0. 01331'ns=1. 65128; vs=38. 3 R1o=+0. 294946 1u= 2. 208133 as=0. 00000 Cementedsurface Rn=+0. 294946 1=+2. 351278 ds=0. 15048 m=l. 69350; =53. 39 R1z=0. 540087 1p1a=+1. 284052 The above data show:

% of the equivalent focal length and comprising on the side of thelonger conjugate a diverging, meniscusshaped front member, the surfacesof which are concave toward the diaphragm; said front member beingspaced total objective, in the pair of vicinal surfaces, formed by therear surface of said strongly refractive converging lens and the frontsurface of said diverging lens of unequal curvature, between thisconverging lens and this diverging lens, being carried out in such amanner that the absolute value of thesum of surface refractive powers insaid pair of vicinal surfaces is larger than A of the equivalentrefractive power of the total system, but does not exceed of saidequivalent refractive power of the total system; the refractive powersshowing tolerances not exceeding and the thicknesses of the lenses, aswell as the air spaces, showing tolerances not exceeding 20.05 withreference to the following data:

wherein R R denote the radii of curvature of the individual lenssurfaces; d d denote the distances between the vertexes of the lenssurfaces; a a denote the axial distances between the individual lenses,n n denote the refractive indices of the lenses, v 11 the Abbe numbersand 1p; face refractive powers, in the direction of the light, thelatter given as multiples of the equivalent refractive power I of thetotal system.

2. A photographic objective of the extended triplet type, having a longback focal length in the range of 85% and 125% of the equivalent focallength and comprising on the side of the longer conjugate a diverging,meniscusshaped front member, the surfaces of which are concave towardthe diaphragm; said front member being spaced from a subsequentconverging system of lenses by a distance which is smaller than 75% ofthe equivalent focal length of the total objective and is greater thanVs of the equivalent focal, length of the total objective; saidsubsequent converging system of lenses consisting of a triplet variationincluding a converging lens additionally inserted on the front side ofsaid triplet variation, followed by a strongly refractive converginglens, which, in turn, is followed by a diverging lens having surfaces ofunequal curvature; distribution of the refractive power within the totalobjective, in the pair of vicinal surfaces, formed by the rear surfaceof said strongly refractive converging lens and the front surface ofsaid diverging lens of unequal curvature, between this converging lensand this diverging lens, being carried out in such a manner that theabsolute value of the sum of surface refractive powers in said pair ofvicinal surfaces is larger than A of the equivalent refractive power ofthe total system, but does (p the Sur- I not exceed =34 of saidequivalent refractive power of the total system; the refractive powersshowing tolerances not exceeding and the thicknesses of the lenses, aswell as the air spaces,

showing the tolerances not exceeding 10.05) with reference to thefollowing data:

wherein R R denote the radii of curvature of the individual lenssurfaces; d d denote the distances between the vertexes of the lenssurfaces; a a denote the axial distances between the individual lenses,n n, denote the refractive indices of the lenses, v v, the Abbe numbersand (p rp the surface refractive powers, in the direction of the light,the latter given as multiples of the equivalent refractive power I ofthe total system.

3. A photographic objective of the extended triplet type, having a longback focal length in the range of and of the equivalent focal length andcom prising on the side of the longer conjugate a diverging,meniscus-shaped front member, the surfaces of which are concave towardthe diaphragm; said front member being spaced from a subsequentconverging system of lenses by a distance which is smaller than 75% ofthe equivalent focal length of the total objective and is greater thanVs of the equivalent focal length of the total objective; saidsubsequent converging system of lenses consisting of a triplet variationincluding a converging lens additionally inserted on the front side ofsaid triplet variation, followed by a strongly refractive converginglens, which, in turn, is followed by a diverging lens having surfaces ofunequal curvature; distribution of the refractive power within the totalobjective, in the pair of vicinal surfaces, formed by the rear surfaceof said strongly refractive converging lens and the front surface ofsaid diverging lens of unequal curvature, between this converging lensand this diverging lens, being carried out in such a manner that theabsolute value of the sum of surface refractive powers in said pair ofvicinal surfaces is larger than A of the equivalent, refractive power ofthe total system, but does not exceed of said equivalent refractivepower of the total system; the refractive powers showing tolerance notexceeding showing tolerances, not exceeding 1005f with reference to thefollowing data:

individual lens surfaces; d d; denote the distances between the vertexesof the lens surfaces; a a, denote the axial distances between theindividual lenses, 1:, n denote the refractive indices of the lenses, v11 the Abbe numbers and (p the surface refractive powers, in thedirection of the light, the latter given as multiples of the equivalentrefractive power 1 of the total system.

4. A photographic objective as claimed in claim 1, in which thediverging meniscus-shaped front member meets the condition wherein D Dand D stand for the curvature distributions, respectively, (a) of saidconverging lens inserted on the front side of the triplet variation, (b)of said first 'lens of the triplet variation and (c) of said second lensof the triplet variation, said curvature distributions being expressedby the quotient of surface powers D r+ p, wherein a, and (p, stand forthe surface refractive powers of the front and rear surfaces,respectively, in the direction of light, of said lenses (a), (b) and(0), respectively. 5. A photographic objective as claimed in claim 2, inwhich the diverging meniscus-shaped front member wherein t stands forthe equivalent refractive power of the total objective-system, (p and(p3 stand for the surface refractive powers of the front surface andrear surface, respectively, of said diverging meniscus shaped frontmember; and the converging lens inserted on the front side of thetriplet variation of the converging system of lenses of the objectiveand the first and second lens, in

the direction of light, of said triplet variation meet the condition 1(PEI 3 4 wherein D D, and D stand for the curvature distributions,respectively, (a) of said converging lens inserted on the front side ofthe triplet variation, (b) of said first lens of the triplet variation,and (c) of said second lens of the triplet variation, said curvaturedistributions being expressed by the quotient of surface powers whereina and (p,- stand for the surface refractive powers of the front and rearsurfaces, respectively, in the direction of light, of said lenses (a),(b) and (c), respectively.

6. A photographic objective as claimed in claim 3, in which thediverging meniscus-shaped front member meets the condition wherein bstands for the equivalent refractive power of the totalobjective-system, 0 and (02 stands for the surface refractive powers ofthe front surface and rear surface, respectively, of said divergingmeniscus shaped front member; and the converging lens inserted on thefront side of the triplet variation of the converging system of lensesof the objective and the first and second lens, in the direction oflight, of said triplet variation meet the condition wherein D,, D, and Dstand for the curvature distributions, respectively, (a) of saidconverging lens inserted on the front side of the triplet variation, (b)of said first lens of the triplet variation, and (c) of said second lensof the triplet variation, said curvature distributions being expressedby the quotient of surface powers wherein (p, and o, stand for thesurface refractive powers of the front and rear surfaces, respectively,in the direction of light, of said lenses (a), (b) and (0),respectively.

References Cited in the file of this patent UNITED STATES PATENTS1,934,561 Rayton Nov. 7, 1933 2,298,853 Warmisham Oct. 13, 19422,649,022 Angenieux Aug. 18, 1953 2,746,351 Tronnier May 22, 19562,826,115 Lange Mar. 11, 1958

